1. Field of the Invention
The present invention relates to an underwater recovery means for recovering unmanned underwater vehicles and more particularly to a means for recovering unmanned underwater vehicles by a submarine through a torpedo launch tube.
2. Description of the Prior Art
The United States Navy has a number of initiatives underway to develop unmanned underwater vehicles (UUVs). The anticipated missions for these vehicles are quite diverse; however, some of the missions require a UUV launch from a submarine to conduct covert operations. The UUV is limited in size in order that it fit within a torpedo tube with enough internal volume to contain a propulsion system, a navigation system, data gathering equipment and other special purpose equipment associated with the particular mission of the UUV. The UUV is launched from the torpedo tube either by the submarine's weapon ejection system or the UUV's own propulsion system.
The United States Navy needs the capability of retrieving these UUVs by a submarine after launch. Retrieval of the UUV is desirable not only because of the UUV's multi-million dollar cost, but also because of the need to retrieve intelligence data the vehicle has gathered and to prepare the vehicle for subsequent missions.
Many options have been considered for submarine retrieval of UUVs. The UUV can be retrieved by attaching it to the outside of the pressure hull but this requires the development of an external retrieval system and increases the ship's acoustic signature. Furthermore, a UUV attached externally to the hull of the submarine is inaccessible for data gathering and maintenance. Scuttling the UUV after it has accomplished its mission is expensive and does not allow retrieval of UUV data gathered during the mission. Using a surface ship to retrieve the UUV destroys the clandestine nature of the UUV's mission and requires that a submarine carry multiple UUVs for multiple covert missions. Use of a line/hook system launched from the torpedo tube to connect with a line/hook system deployed from a returning UUV has also been considered, but this method does not align the returning UUV with the torpedo tube and launchway resulting in possible damage to the UUV or hang up when the UUV is retracted into the ship.
For these reasons, the retrieval means should allow the UUV to be retrieved within the hull of the submarine. Without extensive modification of the submarine, the torpedo tube hatch is the only submarine hull opening with a large enough aperture to allow entry of the UUV upon retrieval. Torpedo tube retrieval is complicated by several factors. Most UUV designs make full use of the space available in the 21 inch diameter torpedo tube leaving little space for a retrieval system in the torpedo tube. UUV designs are weight critical and, therefore, are designed with delicate control surfaces and minimal impact or load carrying capability beyond the loads imposed by hydrodynamic forces. Even under moderate ship speed, a complex flow field exists in the torpedo tube shutter area which exerts significant lateral forces on any vehicle attempting to exit or enter the torpedo launch system's shutterway. The UUV retrieval system must draw the vehicle into the torpedo tube tail first because space within the torpedo room is insufficient to turn the vehicle around for a subsequent launch. Significant ship modifications using a new hull penetration or replacing a major ship component are cost prohibitive.